Setting ElectricCharge as a propellant

To make your engine draw electricity, create a new fuel ratio, and set its Propellant to ElectricCharge. Then enter your desired power draw in kW as its ratio (1kW is 1EC/s in KSP). This ratio will not interfere with other ratios, as it's excluded from standard calculations. That's it! Now your engine should consume electric charge while running.